The present invention relates to an ossicular prosthesis that replaces or bridges at least one component, or parts of a component, of the human ossicular chain, in which the ossicular prosthesis includes, at one end, a first fastening element for mechanical connection to the tympanic membrane or a component of the ossicular chain, in particular to the limb of incus or the manubrium of malleus, and, at the other end, includes a second fastening element for mechanical connection to a further component, or parts of a component, of the ossicular chain, or directly to the inner ear, and includes an elongated connecting element that connects the two fastening elements in a sound-conducting manner, and includes an adjusting device for adjusting the axial length of the ossicular prosthesis in the axial direction of the elongated connecting element, the first fastening element being mechanically rigidly connected to one end, and the second fastening element being mechanically rigidly connected to the other, axially opposed, end of the connecting element.
A device of this type is made known in DE 20 2007 012 217 U1.
Ossicular prostheses are used in cases in which the ossicles of the human middle ear are missing or damaged, either entirely or partially, in order to conduct sound or the sound signal from the tympanic membrane to the inner ear. The ossicular prosthesis has two ends. Depending on the specific circumstances, one end of the ossicular prosthesis is fastened to the tympanic membrane, e.g., using a top plate, and the other end of the ossicular prosthesis is fastened, e.g., to the stapes of the human ossicular chain, or it is inserted directly into the inner ear. In the case of the known ossicular prostheses, sound conduction or signal transmission between the tympanic membrane and the inner ear is limited in many cases, because these known ossicular prostheses do not fully replace the natural anatomical formations of the ossicular chain.
Three types of ossicular prostheses that are used particularly frequently are stapes prostheses, partial prostheses, and total prostheses. Stapes prostheses are fixed to the incus, and extend via a piston into the inner ear. Partial prostheses typically bear via a top plate against the tympanic membrane and establish a connection to the head of the stapes. Total prostheses connect the tympanic membrane to the base of the stapes.
One of the main problems that arises in every case of reconstructing the human ossicular chain involves selecting the correct length of prosthesis. The lengths that are required vary within a range of several millimeters, due to differences in anatomy. When an ossicular prosthesis is surgically implanted, it is therefore necessary to have on hand a sufficiently large selection of prostheses having different axial lengths, or it must be possible to reduce the maximum starting length of the ossicular prostheses to the final axial length that is required.
A device, the length of which is adjustable via a clamping effect, for mechanically connecting the driver of an active hearing aid to a coupling point of the ossicular chain is described in DE 199 48 375 A1.
WO 92/18066 A1 describes a self-adjusting, passive ossicular prosthesis that includes a spring mechanism, which is complicated and very costly to manufacture, in the connection between the first and second fastening elements, which makes it possible to continually change the axial length of the prosthesis depending on the relative position of the fastening points in the middle ear. It is therefore not possible to attain a fixed, reproducibly exact length of the prosthesis even though the length is retained after the prosthesis has been surgically implanted in the middle ear. In addition, due to its very special mechanical and geometric design, the known prosthesis requires a great deal of space in the middle ear, thereby rendering it entirely unusable in many cases due to the unique conditions of a particular patient. In addition, due to the design, a considerable amount of permanent pressure builds up between the two fastening points in the middle ear after implantation, which does not exactly promote healing after surgery, and often eventually results in post-operative complications.
A passive ossicular prosthesis that has an axial length that may be varied within certain limits during surgery is described in DE 39 01 796 A1. In that case, the length is changed by bending the connecting element, which is designed as a thin gold wire, and so handling is complicated and relatively inaccurate, thereby rendering it impossible to attain the desired exact axial length of the ossicular prosthesis. In addition, the result that is attained using this technique is not always reproducible, and, once the connecting element has been bent, it is also possible for the adjusted axial length of the ossicular prosthesis to change because the connecting element springs back.
EP 0 998 884 A2 describes a passive ossicular prosthesis, in which the first connecting element, which is designed as an elongated shank, is inserted through a through-bore of the first fastening element, which is designed as a top plate, until a desired shank length between the first and second fastening elements is attained. The shank is then fixed in this position by constricting the through-bore in the top plate, and the part of the shank that extends past the top plate is trimmed off. One therefore easily obtains a prosthesis that has the particular length that is desired or required, and that remains exactly the same, after surgery in particular.
DE 10 2005 010 705 B3 makes known an ossicular prosthesis, in which an intraoperative variability of the prosthesis length is attained by virtue of the fact that the elongated connecting element is designed in the form of a ball chain. During surgery, the ball chain is inserted through a receiving opening in the first fastening element via a certain number of balls. The ball chain is then fixed in the receiving opening of the fastening element using resilient segment elements that clamp onto either side of the ball chain, and the overhanging part of the ball chain that extends through the receiving opening is cut off, and so the prosthesis ultimately has exactly the desired axial length. In a similar manner, the length variability is also attained using an ossicular prosthesis as described in DE 20 2005 015 944 U1, in which case a trimmable ball chain is likewise used as the connecting element, but the receptacle in the first fastening element has a different design.
A further passive ossicular prosthesis having an intraoperatively variable axial length is described in U.S. Pat. No. 3,710,399. In that case, a two-pieced connecting element is used between the two fastening elements; the two-pieced connecting element includes two parallel, straight wire pieces, one of which extends away from the first fastening element, and the second of which extends away from the second fastening element. The two wire pieces may be connected to the particular other wire piece using wire loops at their ends, or they may be inserted into a type of connecting coupling having two parallel longitudinal bores for the two wire pieces. In the first case, it is not possible, however, to exactly adjust the fixing position and, therefore, the relative position of the two wire pieces, thereby rendering it impossible to adjust the length of the prosthesis in an exact and reproducible manner. In the second case, once the wire pieces have been inserted into the connecting coupling, the relative positions of the wire pieces may tilt, flex, or become displaced, thereby likewise making it difficult or impossible to exactly adjust the axial length of the prosthesis.
Another technique for adjusting the length of a passive ossicular prosthesis is made known in DE 10 2005 027 215 A1. This prosthesis is designed exclusively for use in the situation of stapes surgery, and so a plunger-shaped piston is always provided as the second fastening element. A receiving mechanism is located in this piston, into which the shank-shaped connecting element will be inserted in the axial direction. Leaf springs that are spread radially apart by the connecting element have an arresting effect in a desired relative position between the connecting element and the second fastening element. Aside from the fact that an exactly reproducible adjustment of a desired axial length of the prosthesis is therefore not always guaranteed, the scope of application of this ossicular prosthesis is limited to surgery of the stapes, in the case of which a direct connection to the inner ear is attained via the piston. However, if a bell, piston, clip, or flat shoe will be used as the second fastening part, for connection to another part of the ossicular chain, then this known prosthesis is not usable. If the intention is to form a related receiving mechanism in the second fastening part, then, due to geometry, it functions only in a piston and never in bell, flat shoe, or even in a clip.
The variable-length ossicular prosthesis described in DE 297 22 084 U1 likewise covers a scope of application that is greatly limited; instead of a shank-shaped connecting element, this variable-length prosthesis includes three segment elements that may be snapped off in the manner of a stand, one end of which leads into a bell-shaped or piston-shaped body for fastening to the stapes, and the other end of which leads into a top plate for placement against the tympanic membrane. This design may be used exclusively in combination with a plate-type fastening element, i.e., only when coupling to the tympanic membrane. Another disadvantage of this prosthesis is the fact that it does not include a defined shank as the connecting element between the two fastening elements, and so the prosthesis may shift or flex transversely to the longitudinal axis of the prosthesis if axial force is not introduced absolutely exactly.
The ossicular prosthesis described in U.S. Pat. No. 5,554,188 likewise includes a connecting element that is designed as a two-pieced shank, in which the first, rod-shaped section may be inserted into a receiving bore of the second section, which is designed as a receiving part, and may be displaced axially in the bore. To attain a desired axial length of the prosthesis, the rod-shaped first section is trimmed from a maximum starting length to a suitable end length, and it is inserted into the second section until it stops. By designing the inner diameter of the receiving bore accordingly relative to the outer diameter of the first section, a frictional clamping of the first and second sections should bring about a certain fixation of the prosthesis length, the actual fixation being attained by virtue of the fact that the parts of the prosthesis that may move in opposite directions are unable to move very far apart from one another after surgical implantation in the middle ear, due to their being stopped at the two fastening points. It is therefore impossible to ensure that a length of the prosthesis will always remain exactly the same.
In the case of the passive ossicular prosthesis described in US 2003/0097178 A1, the receiving part also includes a cavity that is open in the direction toward the insertion part and extends in the axial direction of the connecting element; the connecting element is designed to have a variable length in the axial direction between the receiving part and the insertion part, and the specific axial lengths of the connecting element of a specific ossicular prosthesis are fixed by clamping the insertion part to the receiving part in a desired relative coaxial insertion position. In principle, it is therefore possible to attain a desired, defined length of the prosthesis even before it is clamped between the two fastening points; this length is also fixedly retained after surgery, e.g., by inserting a second fastening element, which is designed as a piston, through a perforated base of the stapes.
Finally, DE 20 2007 012 217 U1, which was cited above, makes known an ossicular prosthesis of the type in question, in which the clamping force, in the clamped state, between the receiving part and the insertion part is selected to be considerably greater than the maximum external forces that occur naturally in the middle ear in the region of the ossicles. This makes it possible to vary the length of the passive ossicular prosthesis “in situ” or intraoperatively, and large selections of prosthesis having different lengths do not need to be kept on hand during every surgical procedure. In addition, it is particularly simple to adjust the particular length of the prosthesis that is desired, and, therefore, the handling is likewise particularly simple. Due to the selection of the clamping force described above, subsequent, post-operative and undesired changes in length and/or position of the prosthesis are reliably prevented. In addition, this known ossicular prosthesis may be used universally in all feasible types of couplings in the middle ear space, and it is not limited to a certain class of operations, while, e.g., the prosthesis described in above-cited DE 10 2005 027 215 A1 may only be used exclusively in the situation of stapes surgery. However, these advantages are attained via a relatively complicated, mechanical design of the adjusting device in the connecting element of the prosthesis, a level of production outlay that is considerable by nature, and resultant high manufacturing costs.